The problem O-ring assortments for me is they seem to never have the sizes I need for mower engines repairs. I agree that Nitrile rubber is the ones to get as Gadge said. I have heard that these o-rings will go bad even when not used but the kit I have is over 15 yrs old and they are still in good shape.
Here the jets in Nikki carburetors that are held in place with tiny o-rings are needing to replaced but Briggs doesn't supply them and they were very hard to find in bulk. Good news though as Kawasaki does sell them separately. Why install a 12 usd jet when only it needs a 1.45 usd o-ring [my retail prices].
Otherwise it seems OEMs intently use o-rings that are non-standard sizes making the need for us to buy from them only.
